1. Field of the Invention
The present invention relates to an armature structure for a flat motor to be applied to a device for transmitting vibrations to a human body, and particularly to an armature structure for smoothly restarting at any time an armature composed of one or plural coreless armature coils.
2. Related Art
As a device aiming at transmitting vibrations to a human body, various devices are known such as a wireless telephone paging device (hereinafter referred to as a pager), a cellular telephone, a massager for displaying a massage effect by giving a slight vibration to a human body, a signal receiver for a visual and auditory handicapped person and the like, each of which has a built-in-flat motor having an eccentric armature.
As such a flat motor, for example, a flat-type vibration generator as shown in FIGS. 14 and 15 is known (Japanese Patent Laid-Open Publication No.Hei6-205,565). The vibration generator 1 is composed of a circular plate-type field magnet 3 fixed on the bottom of a casing 2, a freely turnable armature 4 arranged so as to face this field magnet 3, and a shaft 5 positioned at the pivot of this armature 4. The armature 4 is made by molding three coils 6a, 6b and 6c arranged in the shape of an inverse fan together with a resin frame 7 into one body. The armature 4 is provided with commutators 8 to turn together with the coils 6a, 6b and 6c, and these commutators 8 are brought into contact with two electrode brushes 9 extending from the bottom of the casing 2 and thereby the polarities of the three coils 6a, 6b and 6c are alternately switched over, and every switchover of the polarities generates an attractive force and a repulsive force between the armature and the field magnet 3, and therefore the armature 4 continues turning. Particularly in case of using such a flat motor as a vibration generator, since the armature is turned having a great centrifugal force by making the armature 4 itself greatly eccentric as described above, a strong vibration is generated all over the device.
In recent years miniaturization of a pager, a cellular phone, a massager, a signal receiver for a visual and auditory handicapped person and the like has become more and more advanced, and according to this, miniaturizing and lightening of the vibration generator has also become intensely demanded. As described above, however, since a turning force of the armature 4 is generated by repeated alternation of an attractive force and a repulsive force between the coils 6a, 6b and 6c whose polarities are alternately switched over and the field magnet 3, at least three coils 6a, 6b and 6c are necessary. The reason is, as shown in FIG. 16, in the case where the armature 4 is made of a single coil 6 having a central angle of about 90 degrees of rotation, if when the armature 4 is stopped, it comes into one of N and S poles obtained by dividing the magnet 3 into quarters (S pole in FIG. 16), a problem occurs that when attempting to start the armature 4 the next time the armature 4 is not defined in its turning direction and cannot be smoothly started. This is a phenomenon which appears in case where both side portions 6d and 6e of the coil 6 stay within a domain Z on the magnet 3 corresponding to the winding width of the coil 6.
As a result, an object of the present invention is to make it possible to increasingly miniaturize and lighten a flat motor by providing an armature structure in which an armature can be surely and smoothly started to turn even in cases where that the armature is composed of one or two coils.
Another object of the invention is to simplify the manufacturing process of an armature and reduce its manufacturing cost by decreasing the number of coils to form the armature.